Since old times, the fabrication of structures has been performed using welding technology. Structures to be manufactured by welding include not only large structures such as ships and bridges, but also precision machines, as exemplified by bodies of automobiles and trains and impellers of rotating machines. For rotating machines such as pumps, compressors and turbines, in recent years, with the size reduction and high performance of the machines, an tip-opening between a hub and a cover (see an tip-opening b2 between a hub and a cover in FIG. 7(D)) has become narrow and the precision requirement has become strict.
When the tip-opening between the hub and the cover is several tens of millimeters or narrower, it is not possible to insert a welding rod to the back of a blade (in the deep direction with respect to the paper plane in the case of FIG. 7(D)), and therefore, it is difficult to apply a normal welding. In response, conventionally, in the case of welding a blade in such a narrow tip-opening that it is not possible to insert the welding rod to the back of the blade, a slot welding is used